A number of devices are known which provide mobile telecommunication capabilities. Further, known position detection systems employ the known Global Positioning System (GPS), Global Orbiting Navigational System (GLONASS), Loran, RF triangulation, inertial frame reference and Cellular Telephone base site, e.g., time difference of arrival (TDOA) or nearest antenna proximity systems. Known GPS mobile systems include memory to record location, time and event type, and some systems may be integrated with global information systems, to track path, speed, etc. Known Differential GPS (DGPS) systems include mobile telecommunication functionality to communicate between distant units, typically to allow very precise relative position measurements, in the presence of substantial absolute position errors, or to calibrate the position of a mobile transceiver based on a relative position with respect to a fixed transceiver having a known location. These systems do not typically intercommunicate event information between units. Thus, the communications streams relate to position information only. However, known weather balloon transceiver systems, for example, do transmit both position and weather information to a base station.
Many electronic location determination systems are available, or have been proposed, to provide location information to a user equipped with a location determination receiver. Ground-based location determination systems, such as Loran, Omega, TACAN, Decca, U.S. Airforce Joint Tactical Information Distribution System (JTIDS Relnav), or U.S. Army Position Location and Reporting System (PLRS), use the intersection of hyperbolic surfaces to provide location information. A representative ground system is LORAN-C discussed in LORAN-C User Handbook, Department of Transportation, U.S. Coast Guard, Commandant Instruction M16562.3, May 1990, which is incorporated by reference herein. LORAN-C provides a typical location accuracy of approximately 400 meters. A limitation of a LORAN-C location determination system is that not all locations in the northern hemisphere, and no locations in the southern hemisphere, are covered by LORAN-C. A second limitation of LORAN-C is that the typical accuracy of approximately 400 meters is insufficient for many applications. A third limitation of LORAN-C is that weather, local electronic signal interference, poor crossing angles, closely spaced time difference hyperbolas, and skywaves (multipath interference) frequently cause the accuracy to be significantly worse than 400 meters.
Other ground-based location determination devices use systems that were developed primarily for communications, such as cellular telephone, FM broadcast, and AM broadcast. Some cellular telephone systems provide estimates of location, using comparison of signal strengths from three or more sources. FM broadcast systems having subcarrier signals can provide estimates of location by measuring the phases of the subcarrier signals. Kelley et al. in U.S. Pat. No. 5,173,710 disclose a system that allows determination of a location of a vehicle. FM subcarrier signals are received from three FM radio stations with known locations but unknown relative phases by signal processors at the vehicle as well as at a fixed station having a known location. The fixed station processor determines the relative phase of the signals transmitted by the three FM radio stations and transmits the relative phase information to the vehicle. The vehicle processor determines its location from the FM subcarrier signal phases and from the relative phase information it receives. A limitation of cellular systems and FM subcarrier systems for location determination is that they are limited to small regions, with diameters of the order of 20-50 km.
Satellite-based location determination systems such as GPS and GLONASS, use the intersection of spherical surface areas to provide location information with a typical (selective availability) accuracy of 100 meters, anywhere on or near the surface of the earth. These systems may also be used to obtain positional accuracies within 1 centimeter. The satellite-based location determination systems include satellites having signal transmitters to broadcast location information and control stations on earth to track and control the satellites. Location determination receivers process the signals transmitted from the satellites and provide location information to the user.
The Global Positioning System (GPS) is part of a satellite navigation system developed by the United States Defense Department under its NAVSTAR satellite program. A fully operational GPS includes up to 24 satellites approximately uniformly dispersed around six circular orbits with four satellites each, the orbits being inclined at an angle of 55°, relative to the equator, and being separated from each other by multiples of 60° longitude. The orbits have radii of 26,560 kilometers and are approximately circular. The orbits are non-geosynchronous, with 0.5 sidereal day (11.967 hours) orbital time intervals, so that the satellites move with time, relative to the Earth below. Theoretically, four or more GPS satellites will have line of sight to most points on the Earth's surface, and line of sight access to three or more such satellites can be used to determine an observer's position anywhere on the Earth's surface, 24 hours per day. Each satellite carries a cesium or rubidium atomic clock to provide timing information for the signals transmitted by the satellites. Internal clock correction is provided for each satellite clock.
A second configuration for global positioning is GLONASS, placed in orbit by the former Soviet Union and now maintained by the Russian Republic. GLONASS also uses 24 satellites, distributed approximately uniformly in three orbital planes of eight satellites each. Each orbital plane has a nominal inclination of 64.8° relative to the equator, and the three orbital planes are separated from each other by multiples of 120° longitude. The GLONASS circular orbits have smaller radii, about 25,510 kilometers, and a satellite period of revolution of 8/17 of a sidereal day (11.26 hours). A GLONASS satellite and a GPS satellite will thus complete 17 and 16 revolutions, respectively, around the Earth every 8 sidereal days. The signal frequencies of both GPS and GLONASS are in L-band (1 to 2 GHz).
Because the signals from the satellites pass through the troposphere for only a short distance, the accuracy of satellite location determination systems such as GPS or GLONASS is largely unaffected by weather or local anomalies. A limitation of GLONASS is that it is not clear that the Russian Republic has the resources to complete and to maintain the system for full world wide 24 hour coverage.
The inherent accuracy of the GPS position measured by a commercial GPS receiver is approximately 20 meters. However, the United States Government currently intentionally degrades the accuracy of GPS computed positions for commercial users with Selective Availability, SA. With SA, the GPS position accuracy of a commercial GPS receiver is approximately 100 meters. However, higher accuracy is available with the use of secret decryption codes.
Differential Global Positioning System, DGPS, is a technique for enhancing the accuracy of the GPS position, and of course may be applied to GLONASS as well. The DGPS comprises the Global Positioning System together with a GPS reference station receiver situated at a known position. DGPS error correction information is derived by taking the difference between the measurements made by the GPS reference station and the expected measurement at the known position of the reference station. DGPS error correction information can be in the form of GPS satellite pseudorange offsets or GPS position offsets. If GPS position offsets are used, the GPS satellites used in the calculation of the GPS position must be included as part of the DGPS error correction information. A processor in a “differential-ready” GPS receiver applies the DGPS error correction information to enhance the GPS position to an accuracy in the range of 10 meters to a less than one meter.
Two types of DGPS exist, postprocessed and realtime. In postprocessed systems, the DGPS error correction information and a user's GPS position information are processed after the user has completed his data acquisition. In realtime systems, the DGPS error correction information is transmitted to the GPS user in a DGPS telemetry stream, e.g., a radio wave signal, and processed by a differential-ready GPS receiver as the application progresses. Realtime processing is desirable for many applications because the enhanced accuracy of DGPS is available to the GPS user while in the field. Realtime broadcast of DGPS error correction information is available from many sources, both public and private, including Coast Guard RDF beacon and commercially operated FM broadcast subcarriers. A DGPS radio wave receiver is required to receive the DGPS radio wave signal containing the DGPS error correction information, and pass the DGPS error corrections to the differential-ready GPS receiver.
Many applications of GPS including mineral surveying, mapping, adding attributes or features to maps, finding sites on a map, vehicle navigation, airplane navigation, marine navigation, field asset management, geographical information systems, and others require the enhanced accuracy that is available with DGPS. For instance, a 20 to 100 meter error could lead to unintentional trespassing, make the return to an underground asset difficult, or put a user on the wrong block while walking or driving in a city. These applications require a computer to store and process data, retain databases, perform calculations, display information to a user, and take input from a user entry. For instance, the user may need to store a map database, display a map, add attributes to features on the map, and store these attributes for geographical information. The user may also need to store and display locations or calculate range and bearing to another location.
GPS is typically used by many professionals engaged in navigation and surveying fields such as marine navigation, aircraft piloting, seismology, boundary surveying, and other applications where accurate location is required or where the cost of GPS is small compared to the cost of a mistake in determining location. Some mobile professionals in the utilities, insurance, ranching, prospecting, ambulance driving, trucking, delivery, police, fire, real estate, forestry, and other mobile applications use GPS to save time in their work. GPS is also used for personal travel such as hiking, biking, horseback riding, yachting, fishing, driving in personal cars, and other travel activities. To enhance the usefulness of GPS a number of sources have integrated maps into the output, or provide a global information system (GIS) to process the GPS output. Thus, it is known to sort and display proximate map features and/or attributes in the same coordinate system as the position information.
As disclosed in U.S. Pat. No. 5,528,248, incorporated herein by reference, a satellite location determination system using Global Positioning System (GPS) satellite signal transmitters receives a spread spectrum L1 carrier signal having a frequency=1575.42 MHz. The L1 signal from each satellite signal transmitter is binary phase shift key (BPSK) modulated by a Coarse/Acquisition (C/A) pseudo-random noise (PRN) code having a clock or chip rate of f0=1.023 MHz. Location information is transmitted at a rate of 50 baud. The PRN codes allow use of a plurality of GPS satellite signal transmitters for determining an observer's position and for providing location information. A signal transmitted by a particular GPS satellite is selected by generating and correlating the PRN code for that particular satellite signal transmitter with a GPS signal received from that satellite. All C/A PRN codes used for GPS satellite signals are known and are stored and/or generated in a GPS receiver. A bit stream from the GPS satellite signal transmitter includes an ephemeris location of the GPS satellite signal transmitter, an almanac location for all GPS satellites, and correction parameters for ionospheric signal propagation delay, and clock time of the GPS satellite signal transmitter. Accepted methods for generating the C/A-code are set forth in the document GPS Interface Control Document ICD-GPS-200, published by Rockwell International Corporation, Satellite Systems Division, Revision A, 26 Sep. 1984, which is incorporated by reference herein.
Energy on a single carrier frequency from all of the satellites is transduced by the receiver at a point close to Earth. The satellites from which the energy originated are identified by modulating the carrier transmitted from each satellite with pseudorandom type signals. In one mode, referred to as the coarse/acquisition (C/A) mode, the pseudorandom signal is a gold code sequence having a chip rate of 1.023 MHz; there are 1,023 chips in each gold code sequence, such that the sequence is repeated once every millisecond (the chipping rate of a pseudorandom sequence is the rate at which the individual pulses in the sequence are derived and therefore is equal to the code repetition rate divided by the number of members in the code; one pulse of the noise code is referred to as a chip).
The 1.023 MHz gold code sequence chip rate enables the position of the receiver responsive to the signals transmitted from four of the satellites to be determined to an accuracy of approximately 60 to 300 meters.
There is a second mode, referred to as the precise or protected (P) mode, wherein pseudorandom codes with chip rates of 10.23 MHz are transmitted with sequences that are extremely long, so that the sequences repeat no more than once per week. In the P mode, the position of the receiver can be determined to an accuracy of approximately 16 to 30 meters. However, the P mode requires Government classified information about how the receiver is programmed and is intended for use only by authorized receivers. Hence, civilian and/or military receivers that are apt to be obtained by unauthorized users are not responsive to the P mode.
To enable the receivers to separate the C/A signals received from the different satellites, the receiver includes a plurality of different locally derived gold code sources, each of which corresponds with the gold code sequence transmitted from one of the satellites in the field of the receiver. The locally derived and the transmitted gold code sequences are cross correlated with each other over one millisecond, gold code sequence intervals. The phase of the locally derived gold code sequences vary on a chip-by-chip basis, and then within a chip, until the maximum cross correlation function is obtained. Since the cross correlation for two gold code sequences having a length of 1,023 bits is approximately 16 times as great as the cross correlation function of any of the other combinations of gold code sequences, it is relatively easy to lock the locally derived gold code sequence onto the same gold code sequence that was transmitted by one of the satellites.
The gold code sequences from at least four of the satellites in the field of view of the receiver are separated in this manner by using a single channel that is sequentially responsive to each of the locally derived gold code sequences or by using parallel channels that are simultaneously responsive to the different gold code sequences. After four locally derived gold code sequences are locked in phase with the gold code sequences received from four satellites in the field of view of the receiver, the position of the receiver can be determined to an accuracy of approximately 60 to 300 meters.
The approximately 60 to 300 meter accuracy of GPS is determined by (1) the number of satellites transmitting signals to which the receiver is effectively responsive, (2) the variable amplitudes of the received signals, and (3) the magnitude of the cross correlation peaks between the received signals from the different satellites.
In response to reception of multiple pseudorange noise (PRN) signals, there is a common time interval for some of the codes to likely cause a degradation in time of arrival measurements of each received PRN due to the cross correlations between the received signals. The time of arrival measurement for each PRN is made by determining the time of a peak amplitude of the cross correlation between the received composite signal and a local gold code sequence that is identical to one of the transmitted PRN. When random noise is superimposed on a received PRN, increasing the averaging time of the cross correlation between the signal and a local PRN sequence decreases the average noise contribution to the time of arrival error. However, because the cross correlation errors between the received PRN's are periodic, increasing the averaging time increases both signal and the cross correlation value between the received PRN's alike and time of arrival errors are not reduced.
The GPS receiver may incorporate a Kalman filter, which is adaptive and therefore automatically modifies its threshold of acceptable data perturbations, depending on the velocity of the vehicle (GPS antenna). This optimizes system response and accuracy of the GPS system. Generally, when the vehicle increases velocity by a specified amount, the GPS Kalman filter will raise its acceptable noise threshold. Similarly, when the vehicle decreases its velocity by a specified amount, the GPS Kalman filter will lower its acceptable noise threshold.
Extremely accurate GPS receivers depend on phase measurements of the radio carriers that they receive from various orbiting GPS satellites. Less accurate GPS receivers simply develop the pseudoranges to each visible satellite based on the time codes being sent. Within the granularity of a single time code, the carrier phase can be measured and used to compute range distance as a multiple of the fundamental carrier wavelength. GPS signal transmissions are on two synchronous, but separate, carrier frequencies “L1” and “L2”, with wavelengths of nineteen and twenty-four centimeters, respectively. Thus within nineteen or twenty-four centimeters, the phase of the GPS carrier signal will change 360° (2π radians). However, the number of whole cycle (360°) carrier phase shifts between a particular GPS satellite and the GPS receiver must be resolved. At the receiver, every cycle will appear essentially the same, over a short time frame. Therefore there is an “integer ambiguity” in the calculation. The resolution of this integer ambiguity is therefore a calculation-intensive arithmetic problem to be solved by GPS receivers. The traditional approaches to such integer ambiguity resolution have prevented on-the-fly solution measurement updates for moving GPS receivers with centimeter accurate outputs. Very often, such highly accurate GPS receivers have required long periods of motionlessness to produce a first and subsequent position fix.
There are numerous prior art methods for resolving integer ambiguities. These include integer searches, multiple antennas, multiple GPS observables, motion-based approaches, and external aiding. Search techniques often require significant computation time and are vulnerable to erroneous solutions or when only a few satellites are visible. More antennas can improve reliability considerably. If carried to an extreme, a phased array of antennas results, whereby the integers are completely unambiguous and searching is unnecessary. But for economy, reduced size, complexity and power consumption, the minimum number of antennas required to quickly and unambiguously resolve the integers, even in the presence of noise, is preferred.
One method for integer resolution is to make use of the other observables that modulate a GPS timer. The pseudo-random code imposed on the GPS satellite transmission can be used as a coarse indicator of differential range, although it is very susceptible to multipath problems. Differentiating the L1 and L2 carriers in phase sensitive manner provides a longer effective wavelength, and reduces the search space, i.e., an ambiguity distance increased from 19 or 24 centimeters to about 456 centimeters. However, dual frequency receivers are expensive because they are more complicated. Motion-based integer resolution methods make use of additional information provided by platform or satellite motion. But such motion may not always be present when it is needed. Another prior art technique for precision attitude determination and kinematic positioning is described by Hatch, in U.S. Pat. No. 4,963,889, incorporated herein by reference, which employs two spaced antennas, moveable with respect to each other. Knight, U.S. Pat. No. 5,296,861, incorporated herein by reference, provides a method of reducing the mathematical intensity of integer ambiguity resolution. See also, U.S. Pat. No. 5,471,218, incorporated herein by reference.
Direct range measurements, combined with the satellite geometry, may also allow the correct integer carrier phase ambiguities to be determined for a plurality of satellites tracked at two or more sites. The use of additional sensors, such as a laser level, electronic distance meter, a compass, a tape, etc., provide valuable constraints that limit the number of possible integer ambiguities that need to be considered in a search for the correct set.
Many systems using handheld computers, having software and databases defining maps and running standard operating systems, have been coupled to GPS Smart Antennas. Wireless, infrared, serial, parallel, and PCMCIA interfaces have been used to interconnect the handheld computer and the GPS Smart Antenna. Differential-ready GPS Smart Antennas having an input to receive signals representative of DGPS error corrections are also commercially available. Further, GPS receivers and Differential-ready GPS Smart Antennas which are self contained, built onto a type II PCMCIA card (PC Card), and/or having serial data communications ports (RS-232 or RS-422) are commercially available. See, U.S. Pat. Nos. 5,276,451, and 5,210,540, assigned to Pioneer Electronic Corporation.
There are several different types of vehicle navigational systems. The first system makes use of stored map displays wherein the maps of a predetermined area are stored in the in-vehicle computer and displayed to the vehicle operator or driver. The maps, combined with information describing the location where the vehicle started and where it is to go, will highlight the direction and the driver will have to read the display and follow the route. One such stored map display system was offered by General Motors on their 1994 Oldsmobile, using Global Positioning System (GPS) satellites and dead reckoning techniques, and likely map matching to determine a precise location. The vehicle has radio receivers for receiving data from satellites, giving the location of the receiver expressed in latitude and longitude. The driver enters details of the desired destination into an on-board or in-vehicle computer in the form of specific address, a road intersection, etc. The stored map is displayed, allowing the operator to pinpoint the desired destination. The on-board computer then seeks to calculate the most efficient route, displaying the distance to, and the direction of, each turn using graphics and a voice prompt.
Other known systems employ speech recognition as a user input. For example, another system, described in U.S. Pat. No. 5,274,560 does not use GPS and has no sensing devices connected to the vehicle. The routing information is contained in a device that is coupled to a CD player in the vehicle's audio system. Commands are entered into the system via a microphone and the results are outputted through the vehicle's speakers. The vehicle operator spells out the locations and destinations, letter by letter. The system confirms the locations by repeating whole words. Once the system has received the current location and destination, the system develops the route and calculates the estimated time. The operator utilizes several specific performance commands, such as “Next”, and the system then begins to give segment by segment route directions.
Still another system, such as the Siemens Ali-Scout™ system, requires that the driver key-in the destination address coordinates into the in-vehicle computer. A compass located in the vehicle then gives a “compass” direction to the destination address. Such a compass direction is shown in graphics as an arrow on a display unit, indicating the direction the driver should go. Along the side of the road are several infrared beacon sites which transmit data information to a properly equipped vehicle relative to the next adjacent beacon site. From all of the information received, the in-vehicle computer selects the desired beacon data information to the next beacon and displays a graphic symbol for the vehicle operator to follow and the distance to the desired destination. In this system, there is no map to read; both a simple graphic symbol and a segment of the route is displayed, and a voice prompt telling the vehicle operator when to turn and when to continue in the same direction is enunciated. Once the program begins, there is minimal operator feedback required.
U.S. Pat. No. 4,350,970, describes a method for traffic management in a routing and information system for motor vehicle traffic. The system has a network of stationary routing stations each located in the vicinity of the roadway, which transmit route information and local information concerning its position to passing vehicles. The trip destination address is loaded by the vehicle operator into an onboard device in the vehicle and by dead reckoning techniques, a distance and direction graphic message is displayed. The first routing station which the vehicle passes transmits a message to the vehicle with route data to the next routing station. The vehicle receives the message and as it executes the several vector distances in the message, it accumulates time and distance which it then transmits to the second routing station when it is interrogated by the second routing station. In this manner, traffic management is updated in real time and the vehicles are always routed the “best way”. Of course, the best way may be the shortest way, the less traveled way, the cheapest way or any combination of these plus other criteria. See also, U.S. patent application Ser. No. 08/258,241, filed on Aug. 3, 1994.
U.S. Pat. No. 5,668,880, incorporated herein by reference, relates to an intervehicle data communication device.
Systems which integrate GPS, GLONASS, LORAN or other positioning systems into vehicular guidance systems are well known, and indeed navigational purposes were prime motivators for the creation of these systems. Radar, laser, acoustic and visual sensors have all been applied to vehicular guidance and control, as well. For example, U.S. Pat. No. 4,757,450 relates to a reflected beam system for detecting a preceding vehicle, in order to allow control over intervehicular spacing. U.S. Pat. No. 4,833,469 relates to an obstacle proximity sensor, employing, e.g., a radar beam to determine distance and relative velocity of an obstacle. U.S. Pat. No. 5,600,561 relates to a vehicle distance data processor which computes a velocity vector based on serial timepoints. U.S. Pat. No. 4,552,456 relates to an optical pulse radar for an automobile. U.S. Pat. No. 4,543,577 relates to a moving obstacle detection system for a vehicle, using Doppler radar. U.S. Pat. No. 4,349,823 relates to an automotive radar system for monitoring objects in front of the vehicle. U.S. Pat. No. 5,473,538 relates to a collision judging system for a vehicle, triggered by a braking event and determining a distance to an obstacle in front of the vehicle. U.S. Pat. No. 4,168,499 relates to an anti-collision radar system. U.S. Pat. No. 4,626,850 relates to a vehicle detection and collision avoidance apparatus, using an acoustic sensor. U.S. Pat. No. 4,028,662 relates to a passing vehicle signaling apparatus, to detect adjacent vehicles during a lane change. U.S. Pat. No. 5,541,590 relates to a vehicle crash predictive and evasive system, employing neural networks. U.S. Pat. No. 5,646,612 relates to a vehicle collision avoidance system, using an infrared imaging system. U.S. Pat. No. 5,285,523 relates to a neural network system for recognizing driving conditions and controlling the vehicle in dependence thereon. U.S. Pat. No. 5,189,619 relates to an artificial intelligence based adaptive vehicle control system. U.S. Pat. No. 5,162,997 relates to a driver-adaptive automobile control system. U.S. Pat. No. 3,689,882 relates to an anti-collision radar system for detecting obstacles or on-coming vehicles.
U.S. Pat. No. 4,855,915 relates to a vehicle which may be autonomously guided using optically reflective materials. U.S. Pat. No. 5,347,456 relates to an intelligent roadway reference system for controlling lateral position of a vehicle, using magnetic sensors. U.S. Pat. No. 5,189,612 relates to an autonomous vehicle guidance system employing buried magnetic markers. U.S. Pat. No. 5,039,979 relates to a roadway alarm system employing metallized painted divider lines. U.S. Pat. No. 4,239,415 relates to a method for installing an electromagnetic sensor loop in a highway. U.S. Pat. No. 4,185,265 relates to a vehicular magnetic coded signaling apparatus which transmits binary signals using magnetic signposts. U.S. Pat. No. 5,687,215 relates to a vehicular emergency message system. U.S. Pat. No. 5,550,055 relates to a position monitoring system for vehicles, for example in case they are stolen. U.S. Pat. No. 5,563,071 relates to a system for time and/or event logging of an event, employing differential GPS. U.S. Pat. No. 5,701,328 relates to a chirped spread spectrum positioning system.
U.S. Pat. Nos. 5,689,269, 5,119,504, 5,678,182, 5,621,793, 5,673,305, 5,043,736, 5,684,860, 5,625,668, 5,602,739, 5,544,225, 5,461,365, 5,299,132, 5,301,368, 5,633,872, 5,563,607, 5,382,957, 5,638,078, 5,630,206, 5,610,815, 4,677,555, 4,700,301, 4,807,131, 4,963,889, 5,030,957, 5,144,317, 5,148,179, 5,247,306, 5,296,861, 5,347,286, 5,359,332, 5,442,363, 5,451,964, expressly incorporated herein by reference, relate to systems which employ GPS and telecommunication functionality. Such systems are often employed in differential global positioning system (DGPS) and vehicular security and tracking applications.
Typical “secure” encryption systems include the Rivest-Shamir-Adelman algorithm (RSA), the Diffie-Hellman algorithm (DH), the Data Encryption Standard (DES), elliptic curve encryption algorithms, so-called PGP algorithm, and other known algorithms. U.S. Pat. Nos. 4,200,770, 4,218,582, 4,405,829, 4,424,414 and 4,424,415, expressly incorporated herein by reference, relate to RSA-type encryption systems. Other cryptographic system patents include U.S. Pat. Nos. 4,658,094 and 4,797,920, incorporated herein by reference. See also:    “A Method for Obtaining Digital Signatures and Public-Key Cryptosystems.” By R. L. Rivest, A. Shamir, and L. Adelman, Communication of the ACM, February 1978, Volume 21 Number 2. Pages 120-126.    The Art of Computer Programming, Volume 2: Seminumerical Algorithms, By D. E. Knuth, Addison-Wesley, Reading, Mass. 1969.    “The First Ten Years of Public Key Cryptography”, By Whitfield Diffie, Proceedings of the IEEE, Volume 6 Number 5, May 1988, Pages 560-577.    U.S. Pat. Nos. 4,668,952; 4,698,632; 4,700,191; 4,709,407; 4,725,840; 4,750,215; 4,791,420; 4,801,938; 4,805,231; 4,818,997; 4,841,302; 4,862,175; 4,887,068; 4,939,521; 4,949,088; 4,952,936; 4,952,937; 4,954,828; 4,961,074; 5,001,777; 5,049,884; 5,049,885; 5,063,385; 5,068,663; 5,079,553; 5,083,129; 5,122,802; 5,134,406; 5,146,226; 5,146,227; 5,151,701; 5,164,729; 5,206,651; 5,239,296; 5,250,951, 5,268,689; 5,270,706; 5,300,932; 5,305,007; 5,315,302; 5,317,320; 5,331,327; 5,341,138; 5,347,120; 5,363,105; 5,365,055; 5,365,516; 5,389,930; 5,410,750; 5,446,923; 5,448,638; 5,461,383; 5,465,413; 5,513,110; 5,521,696; 5,525,989; 5,525,996; 5,528,245; 5,528,246; 5,529,139; 5,510,793; 5,529,139; 5,610,815, expressly incorporated herein by reference, relate to radar and radar detection and identification systems, and associated technologies.    U.S. Pat. No. 5,519,718, incorporated herein by references, relates to a mobile bidirectional pager communication scheme.    U.S. Pat. No. 5,218,620, incorporated herein by references, relates to a spread spectrum communication device.    U.S. Pat. Nos. 3,161,871; 3,568,161; 3,630,079; 3,664,701; 3,683,114; 3,769,710; 3,771,483; 3,772,688; 3,848,254; 3,922,673; 3,956,797; 3,986,119; 3,993,955; 4,002,983; 4,010,619; 4,024,382; 4,077,005; 4,084,323; 4,114,155; 4,152,693; 4,155,042; 4,168,576; 4,229,620; 4,229,737; 4,235,441; 4,240,079; 4,244,123; 4,274,560; 4,313,263; 4,323,921; 4,333,238; 4,359,733; 4,369,426; 4,384,293; 4,393,270; 4,402,049; 4,403,291; 4,428,057; 4,437,151; 4,445,118; 4,450,477; 4,459,667; 4,463,357; 4,471,273; 4,472,663; 4,485,383; 4,492,036; 4,508,999; 4,511,947; 4,514,665; 4,518,902; 4,521,885; 4,523,450; 4,529,919; 4,547,778; 4,550,317; 4,555,651; 4,564,085; 4,567,757; 4,571,847; 4,578,678; 4,591,730; 4,596,988; 4,599,620; 4,600,921; 4,602,279; 4,613,867; 4,622,557; 4,630,685; 4,633,966; 4,637,488; 4,638,445; 4,644,351; 4,644,368; 4,646,096; 4,647,784; 4,651,157; 4,652,884; 4,654,879; 4,656,463; 4,656,476; 4,659,970; 4,667,203; 4,673,936; 4,674,048; 4,677,555; 4,677,686; 4,678,329; 4,679,147; 4,680,715; 4,682,953; 4,684,247; 4,688,244; 4,690,610; 4,691,149; 4,691,385; 4,697,281; 4,701,760; 4,701,934; 4,703,444; 4,706,772; 4,709,195; 4,713,767; 4,718,080; 4,722,410; 4,727,492; 4,727,962; 4,728,922; 4,730,690; 4,731,613; 4,740,778; 4,741,245; 4,741,412; 4,743,913; 4,744,761; 4,750,197; 4,751,512; 4,751,983; 4,754,280; 4,754,283; 4,755,905; 4,758,959; 4,761,742; 4,772,410; 774,671; 4,774,672; 4,776,750; 4,777,818; 4,781,514; 4,785,463; 4,786,164; 4,790,402; 4,791,572; 4,792,995; 4,796,189; 4,796,191; 4,799,062; 4,804,893; 4,804,937; 4,807,714; 4,809,005; 4,809,178; 4,812,820; 4,812,845; 4,812,991; 4,814,711; 4,815,020; 4,815,213; 4,818,171; 4,819,053; 4,819,174; 4,819,195; 4,819,860; 4,821,294; 4,821,309; 4,823,901; 4,825,457; 4,829,372; 4,829,442; 4,831,539; 4,833,477; 4,837,700; 4,839,835; 4,846,297; 4,847,862; 4,849,731; 4,852,146; 4,860,352; 4,861,220; 4,864,284; 4,864,592; 4,866,450; 4,866,776; 4,868,859; 4,868,866; 4,869,635; 4,870,422; 4,876,659; 4,879,658; 4,882,689; 4,882,696; 4,884,348; 4,888,699; 4,888,890; 4,891,650; 4,891,761; 4,894,655; 4,894,662; 4,896,370; 4,897,642; 4,899,285; 4,901,340; 4,903,211; 4,903,212; 4,904,983; 4,907,159; 4,908,629; 4,910,493; 4,910,677; 4,912,475; 4,912,643; 4,912,645; 4,914,609; 4,918,425; 4,918,609; 4,924,402; 4,924,417; 4,924,699; 4,926,336; 4,928,105; 4,928,106; 4,928,107; 4,932,910; 4,937,751; 4,937,752; 4,939,678; 4,943,925; 4,945,501; 4,947,151; 4,949,268; 4,951,212; 4,954,837; 4,954,959; 4,963,865; 4,963,889; 4,968,981; 4,970,652; 4,972,431; 4,974,170; 4,975,707; 4,976,619; 4,977,679; 4,983,980; 4,986,384; 4,989,151; 4,991,304; 4,996,645; 4,996,703; 5,003,317; 5,006,855; 5,010,491; 5,014,206; 5,017,926; 5,021,792; 5,021,794; 5,025,261; 5,030,957; 5,030,957; 5,031,104; 5,036,329; 5,036,537; 5,041,833; 5,043,736; 5,043,902; 5,045,861; 5,046,011; 5,046,130; 5,054,110; 5,055,851; 5,056,106; 5,059,969; 5,061,936; 5,065,326; 5,067,082; 5,068,656; 5,070,404; 5,072,227; 5,075,693; 5,077,557; 5,081,667; 5,083,256; 5,084,822; 5,086,390; 5,087,919; 5,089,826; 5,097,269; 5,101,356; 5,101,416; 5,102,360; 5,103,400; 5,103,459; 5,109,399; 5,115,223; 5,117,232; 5,119,102; 5,119,301; 5,119,504; 5,121,326; 5,122,803; 5,122,957; 5,124,915; 5,126,748; 5,128,874; 5,128,979; 5,144,318; 5,146,231; 5,148,002; 5,148,179; 5,148,452; 5,153,598; 5,153,836; 5,155,490; 5,155,491; 5,155,591; 5,155,688; 5,155,689; 5,157,691; 5,161,886; 5,168,452; 5,170,171; 5,172,321; 5,175,557; 5,177,685; 5,184,123; 5,185,610; 5,185,761; 5,187,805; 5,192,957; 5,193,215; 5,194,871; 5,202,829; 5,208,756; 5,210,540; 5,210,787; 5,218,367; 5,220,507; 5,220,509; 5,223,844; 5,225,842; 5,228,695; 5,228,854; 5,245,537; 5,247,440; 5,257,195; 5,260,778; 5,265,025; 5,266,958; 5,269,067; 5,272,483; 5,272,638; 5,274,387; 5,274,667; 5,276,451; 5,278,424; 5,278,568; 5,292,254; 5,293,318; 5,305,386; 5,309,474; 5,317,321; 5,319,548; 5,323,322; 5,324,028; 5,334,974; 5,334,986; 5,347,285; 5,349,531; 5,364,093; 5,365,447; 5,365,450; 5,375,059; 5,379,224; 5,382,957; 5,382,958; 5,83,127; 5,389,934; 5,390,125; 5,392,052; 5,400,254; 5,402,347; 5,402,441; 5,404,661; 5,406,491; 5,406,492; 5,408,415; 5,414,432; 5,416,712; 5,418,537; 5,418,538; 5,420,592; 5,420,593; 5,420,594; 5,422,816; 5,424,951; 5,430,948; 5,432,520; 5,432,542; 5,432,841; 5,433,446; 5,434,574; 5,434,787; 5,434,788; 5,434,789; 5,519,403; 5,519,620; 5,519,760; 5,528,234; 5,528,248; 5,565,874 and Re32,856, expressly incorporated herein by reference, relate to GPS systems and associated technologies.    Foreign patent references CA 1298387, 19920300; CA 1298903, 19920400; CA 2009171/1990 02; DE 3310111, 19840900; DE 3325397/1985 01; DE 3419156, 19840500; DE 3538908A1, 19870500; DE 4123097; EP 0155776/1990 08; EP 0158214, 19851000; EP 0181012, 19860500; EP 0290725/1992 09; EP 0295678, 19880600; EP 0309293A2, 19890300; EP 0323230, 19890500; EP 0323246, 19890700; EP 0348528, 19900100; EP 0393935, 19901000; EP 0444738, 19910900; EP 0485120, 19920500; EP 0501058/1991 04; EP 0512789, 19921100; FR 2554612, 19850500; GB 2079453, 19820100; GB 211204, 19830600; GB 2126040, 19870100; GB 2238870, 19891100; GB 2256987; JP 57-32980, 19820200; JP 63-26529, 19840200; JP 1130299, 19871100; JP 1136300, 19871100; JP 153180, 19890300; JP 63188517, 19890500; JP 0189414, 19900700; JP 2212713, 19900800; JP 02-243984, 19900900; JP 03-17688, 19910100; JP 3-080062, 1991 04 12; JP 3-080063, 1991 04 12; JP 0078678, 19910400; JP 0092714, 19910400; JP 1272656, 19910900; JP 03245075, 19911000; JP 3245076, 19911000; JP 63-12096; JP 221093; WO 87/06713, 19871100; WO 92/08952, 19920500; WO 93/09510, 19930500; WO 87/07056, 19871100 and WO 91/05429, incorporated herein by reference, relate to GPS and related technologies.
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